Potassium keeps your heartbeat regular, and it helps keep your muscles working properly. Potassium is found in lots of fruits and vegetables. Too much potassium can be dangerous to your heart, so you may need to restrict the amount of potassium in your diet if your kidneys are not working properly. Some examples of foods that are high in potassium include bananas, mangoes, cantaloupe, oranges, potatoes, raw carrots, tomatoes, and even peanut butter. Try substituting these items with low-potassium foods, such as apples, blueberries, grapes, pears, strawberries, onions, peppers, cauliflower, and cucumber.